The present invention relates to a roller tunnel kiln for firing articles such as tile bases.
Conventional roller tunnel kilns have been composed of a tunnel-shaped or elongate tubular kiln body made of refractory brick, and a number of article feed rollers extending respectively through a number of holes defined at suitable intervals in opposite side walls of the kiln body, the article feed rollers being rotatable about their own axes but immovable longitudinally of the kiln body.
More specifically, as shown in FIG. 17 of the accompanying drawings, a conventional roller tunnel kiln 1 has porcelain feed rollers 4 extending respectively through a number of insertion holes 3 defined in opposite kiln walls 2a and 2b of a kiln body 2 and spaced at suitable intervals in the longitudinal direction of the kiln walls 2a and 2b. Each of the porcelain rollers 4 has opposite ends mounted on roller supports 5 and 6 disposed one on each side of the kiln body 2.
Roller supports 5 on one side have a number of chain sprockets 5a associated respectively with the rollers 4 in coaxial relation thereto, with a common drive chain 7 being in mesh with the chain sprockets 5a. By driving the drive chain 7, the chain sprockets 5a and hence all of the rollers 4 are rotated about their own axes at a prescribed rotational speed. An article 8 being fired which is placed on the porcelain rollers 4 are fed along successively over the rollers 4. Therefore, the article 8 can be fed along through the kiln.
However, the roller tunnel kiln 1 of the above construction has suffered the following disadvantages:
(1) A porcelain roller 4' with glaze deposits 9 on its surface has to be replaced with a new porcelain roller 4. However, the replacement process is tedious and time-consuming. First, the roller support 6 has to be detached from a bracket 10 in order to pull the roller 4' from the holes 3. Then, the new roller 4 is inserted through the holes 3 until its distal end is mounted on the roller support 5. The other end of the roller 4 is mounted on the roller support 6, which is then secured to the bracket 10. The above process is required for each roller. Therefore, large amount of labor and time is required for replacing porcelain rollers (usually 400 to 500 in number) disposed in a high-temperature firing zone in which the roller surfaces tend to be smeared with glaze deposits melted in a high-temperature atmosphere in the kiln.
(2) When removing the porcelain rollers 4' heated to 1100.degree. to 1300.degree. C. in the high-temperature firing zone in the tunnel kiln out of the holes 3, the rollers 4' are liable to get broken or cracked due to rapid quenching since there is a large temperature difference between the rollers and a temperature outside of the kiln. The same problem occurs when the new porcelain rollers 4 are placed into the high-temperature firing zone in the tunnel kiln since the rollers 4 are rapidly heated. In an actual roller replacement process, therefore, provision should be made for preventing the removed or inserted porcelain rollers from being damaged due to a thermal shock. However, the roller tunnel kiln cannot be put into operation if the temperature in the high-temperature zone falls below a prescribed temperature. With the conventional roller tunnel kiln, a long downtime has been necessary by each roller replacement process, and hence the availability of the kiln has been quite low.
(3) The porcelain roller 4 can easily be broken as it has a weak bending strength and a low shock resistance. Therefore, the porcelain rollers 4 have frequently been broken in the prior roller tunnel kiln. When a porcelain roller 4 is broken while the roller tunnel kiln is in operation, the roller 4 falls making a roller-free space in the succession of rollers. The article 8 having been delivered to the roller-free space, it is either stopped there and will not be advanced, or drops through the roller-free space onto the bottom of the kiln. The conventional practice is therefore that each time any porcelain roller in the kiln is broken, the operation of the roller tunnel kiln should be interrupted, and a new porcelain roller should be mounted in place. Therefore, the rate of production has been poor with the conventional kiln.
(4) The porcelain feed rollers in the roller tunnel kiln are rotated about their own axes for feeding along the article 8 successively thereover. Even if a row of aligned articles 8 is placed onto the feed rollers at the inlet of the tunnel kiln and successively fed into the kiln, the articles as they are fed are displaced out of alignment due to slippage between the surfaces of the rollers 4 and the lower surfaces of the articles 8. The articles 8 thus tend to hit each other and be broken, or a large expenditure of time and labor is required to deliver the articles in a row into an unloader (not shown) at the outlet of the roller tunnel kiln.